Method for preparing waste paper

ABSTRACT

In order for a method for preparing fibres for producing paper from a fibre-containing material, in particular from waste paper, to be improved such that shortening of the fibres separated from the fibre material is reduced to a minimum, it is proposed that the fibre-containing material is supplied in a moist state for pulping and is pulped to a dry state by continuous impact action.

The invention concerns a method for preparing and obtaining fibres for producing paper or similar, such as for example insulating material, from a fibre-containing material, in particular from waste paper. It also concerns the use of this method for document destruction.

Methods for preparation of waste paper are known. In these waste paper is basically dissolved in bundled and possibly pressed form in a pulper. To this end the pulper is filled with water. Then the waste paper or the pulp is introduced and using a propeller dissolved and disintegrated there. In the pulper the paper can also undergo a de-inking process using chemicals. Then the fibrous suspension is pumped out and processed further. The consistency (dry mass of waste paper/(dry mass of waste paper+water)) is approximately 5%. Pulp can also be dissolved with high consistency pulpers. The consistency that can be achieved here is between 12 and 18%. Here the mixture dissolves better, allowing energy and space to be saved. This is due to the fact that because of the higher consistency and the lower water content the shearing forces between the fibres are significantly higher. For pumping out the mixture must then be thinned to a consistency of approximately 5%, however.

After the pulper, rejects that have arisen during the dissolution are separated off.

Then the fibre suspension passes through a deflaker, in which the fibre bundles (specks) are broken down into their individual fibres. This takes place by loosening the external fibre wall layer and serves to increase the degree of swelling of the fibres.

Impurities (sand and so on) are then removed from the fibre suspension in a cleaner before it is passed to a refiner. In the latter the fibres are loosened and possibly disintegrated further.

In the subsequent mixing vat the fibre pulp is first diluted with water from the sieve of a paper machine, and then fillers are also added. Whether these fillers are added here or during sizing in the paper machine depends on the paper's use.

Basically in the method it is to be avoided that the waste paper fibres are shortened or damaged, in particular split in the longitudinal direction, or that the degree of grinding is increased, since the waste paper has already been prepared at least once for paper manufacture. Furthermore, plastic films, plastic parts, sand or similar contained in the waste paper should as far as possible not be broken down, in order that it can subsequently be easily removed.

Nevertheless, further disintegration of the waste paper fibres cannot be completely avoided, so that the waste paper fibres after being recycled between five and seven times are no longer suitable for paper manufacture since they are no longer of sufficient length.

The object of the present invention is to provide a method of the kind already stated at the beginning, in which the shortening of the fibres is minimised.

This object is achieved with a method having the features of claim 1. The sub-claims contain features of preferred embodiments of the method according to the invention.

Here and in the following dry pulping shall mean that the waste paper is not pulped within a suspension in water, and thus water is not used in the pulping of the waste paper as a carrier and means of transport for the waste paper, but that it is pulped in such a way that the waste paper, once it has been pulped by impact action, is present in the form of a solid mixture.

It has surprisingly been discovered that with dry pulping under continuous impact action the swollen fibres of the waste paper are significantly better preserved than with the conventional preparation process using dissolution, deflaking and refiner grinding. Thus the effect of the impact, in particular if it is intensive and pulsating, is to transfer energy pulses to the waste paper, leading to friction between the fibres or between the fibres and the fillers of the waste paper. As a result the fibres are released from one another and inter alia released from fillers and debris. At the same time the fibres are roughened allowing them to crosslink with one another particularly well during paper manufacture.

This works in a particularly efficient and fibre-preserving way if the waste paper fibres contained in the waste paper prior to pulping have already been swollen, preferably completely swollen. In particular this allows the fibrils already contained in the fibres to be preserved, such that renewed fibrillation, for example in a refiner, can be dispensed with. In addition, with sufficient friction or energy introduced via the impacts or shocks, enough heat can be generated for the water contained in the bundled fibres to briefly evaporate, although the resulting vapour bubbles collapse again. With the resultant hard cavitation (vapour shock) achieved a significant contribution can be made to the separation of the fibres from one another or of the additives or pollutants from the fibres to be recovered.

Here the consistency of the waste paper to be pulped is advantageously in a range of 40% to 99%, preferably between 50% and 95% and particularly preferably between 80% or 85% and 95%. Thus the consistency is quite significantly higher than the consistency of up to 18% when waste paper is dissolved in aqueous dispersion.

In order to regulate the humidity of the waste paper during pumping, but also to control the temperature during pulping and furthermore for bonding of dust it is advantageous if at the container in which the waste paper is pulped a device is provided for injecting or spraying water. Temperature regulation is achieved here through the evaporative heat loss caused by the water.

The waste paper is preferably, unlike when feeding a pulper, introduced into the container for pulping without wires to hold the bales together, since these are not needed. In this way the normal pigtail of knotted wires and the coarse substances trapped within them can be avoided.

For generating the impact action one or more, in particular flexible, impact tools are preferably used. One or more driven chains within a container, supported centrally on the base of the container and rotating at high speed, have proven to be particularly effective for this purpose. The pulping of the fibre-containing material takes place very gently in particular if the chain links have a rounded design in all directions, such that they have no corners or edges, which could cause nicks in the fibre material. Cross-flow shredders, in particular, which are used inter alia for breaking up scrap materials such as refrigerators, are particularly suitable for the dry pulping of fibre materials. With a cross-flow shredder having a chain length of 40 cm at between 700 and 1 700 rpm exceptional results have been achieved.

Other tools may also be used to pulp the fibre material, however, thus for example systems working on a rotary principle.

The method according to the invention has, inter alia, the advantage that the additives and debris are dissolved out of the waste paper dry. This has the advantage, firstly, that following pulping of the waste paper these can be separated from the fibres as dry fractions, for example making use of the difference in particle inertia, particle size or particle density, with the help of for example sieves, air separators and/or centrifuges. This can take place actually during (for example using a sieve or air separator) or also after pulping. For example, in the container for pulping the fibre material laterally, preferably in the vicinity of the base of the container, a window with a sieve can be inserted, through which the pulped fibre material can emerge from the container, once it has been disaggregated to a size predetermined by the sieve. Secondly, additives do not have to be separated from the process water as is the case with the preparation of waste paper in aqueous suspension.

The pulped fibre material can, once it has left the container for pulping, be transported via screw conveyors to further processing stations. If during transport any further foreign matter has to be separated from the fibre material, vibration conveyors can be provided for the purpose.

In order to improve the quality of the prepared fibres for the manufacture in particular of strong paper, the fibre-containing material can have kraft fibre paper can be added, which is pulped together with the other fibre material. Kraft fibre paper contains particularly long and stable fibres, the length of which is at least almost completely preserved in the preparation according to the invention. These long fibres in the mixture created of prepared fibres then serve as a kind of reinforcement in the paper ensuring particular strength.

For the preparation of the fibres obtained with the method according to the invention it is then sufficient for them to be mixed with water in a subsequent swelling vat or agitation vat, in order to provide the fibre pulp for paper manufacture.

Trials have shown that the fibres obtained in this way allow an increase in the waste paper recycling cycles from approximately 7 previously to approximately 35.

The method according to the invention also provides further quite significant advantages. Firstly, by dispensing with water as the carrier, energy consumption is significantly reduced since significantly less mass has to be shifted when pulping the waste paper. Thus for the same energy expenditure 18 times the quantity of fibres (with reference to the absolute dry quantity of fibres) can be throughput.

Water consumption is also necessarily lower. And the contact time required between the waste paper and the water it contains is approximately 2 to 4 hours less than in a conventional method with a pulper. As a result the loading of the water with impurities entering into solution such as for example COD or calcium, is significantly reduced.

Finally, it transpires that the method according to the invention can also be used for efficient document destruction. If, for example, a cross-flow shredder is used the paper of the documents to be destroyed is disaggregated and at the same time separated from other components of the documents, for example any metal parts or plastics. In doing so the paper is broken down into its fibres, so that any information printed on it is irretrievably destroyed. The method is superior to any conventional method of document destruction and allows the preparation of the paper material as fibres, which can be directly reused for paper manufacture.

In the following the invention is explained in more detail on the basis of two schematic diagrams, with which the process sequence for preparation of waste paper in aqueous suspension and the process sequence for fibre preparation according to the invention are compared.

FIG. 1 shows the essential steps of a conventional method for waste paper preparation. The pulper 1 is loaded with the fibre material to be prepared and water, so that the fibre material is dissolved. In a subsequent drainage vat 2 and a high-consistency cleaner 3 the suspension pumped from the pulper 1 is cleaned of coarse debris. The remaining fibre material suspension is passed to a deflaker, in which the fibre bundles still present are separated into individual fibres and the fibres disintegrated. In the subsequent cleaning the fine debris is removed, before the remaining cleaned fibre suspension then has the additives necessary for paper manufacture mixed-in in a mixing vat 6. The resulting paper pulp is then passed to the headbox 7 of the paper machine.

The highly efficient process according to the invention, on the other hand, provides merely for an FRT (fibre refreshing technology) reactor, for example in the form of a cross-flow shredder 11, in which moist fibre-containing material without water as the carrier fluid is prepared by impacting of the individual fibres. In a subsequent cleaning 12 the separated, almost entirely dry fractions are separated using a suitable conventional separation method. The fibres produced in this way are then placed in a swelling vat or agitation vat 13, in which the fibres can swell (again) and any additives necessary according to the type of paper to be manufactured can be mixed into the fibre. The pulp produced in the swelling vat 13 is then passed to the headbox 14 of a paper machine.

This comparison clearly shows that apart from the advantages already described, a further advantage is that the system design is significantly simpler and more space-saving and on the basis of the lower number of process steps alone allows a more rapid preparation process. Thus the investment costs and ongoing maintenance costs are more favourable than conventional preparation systems with a pulper. 

1. A method for preparing and obtaining fibres for producing paper or similar from a fibre-containing material, the method including: supplying the fibre-containing material in a moist state; and pulping the fibre-containing material to a dry state by continuous impact action.
 2. The method according to claim 1, wherein a consistency of the fibre-containing material is in the range of 40% to 99%.
 3. The method according to claim 1, further including injecting or spraying water, wherein humidity of the fibre-containing material, temperature, dust generation, or any combination of humidity, temperature, or dust generation, when the fibre-containing material is pulped is controlled by the injecting or spraying water.
 4. The method according to claim 1, wherein the pulping comprises using one or more flexible impact tools.
 5. The method according to claim 4, wherein the pulping takes place in a cross-flow shredder.
 6. The method according to claim 1, further including separating coarse debris and fine debris during or after the pulping.
 7. The method according to claim 1, further including swelling, after the pulping, in a swelling or agitation vat.
 8. The method according to claim 1, further including adding kraft paper to the fibre-containing material, wherein the pulping comprises pulping the kraft paper together with the fibre-containing material.
 9. A method of document destruction, comprising using the method according to claim 1 for the document destruction.
 10. The method according to claim 1, wherein the fibre-containing material comprises waste paper.
 11. The method according to claim 1, wherein a consistency of the fibre-containing material is in the range of at least 50% to 95%.
 12. The method according to claim 1, wherein a consistency of the fibre-containing material is in the range of 85% to 95%. 